Tug barge lightering connection system

ABSTRACT

A lightering connection system is provided for coupling a tug boat to a barge, where the connection permits relative vertical movement between the tug and barge while maintaining horizontal movement control between the vessels. The tug boat has port and starboard retractable rams having coupler heads which engage the barge along inboard port and starboard vertical receiver channels. The coupler heads and vertical receiver channels are provided with waveform surfaces to permit interlocking engagement between the tug boat and barge. The waveform surfaces also permit smooth relative movement of the surfaces as the ram disengages in performing the lightering operation. The coupler heads and vertical channel receivers have a mating angular construction to maintain horizontal movement control between the tug and barge during the lightering operation.

CROSS REFERENCE TO RELATED APPLICATIONS

This present continuation patent application is related to and claims priority benefit of an earlier-filed non-provisional patent application of the same title, Ser. No. 11/345,792, filed Feb. 2, 2006, and an even earlier filed provisional patent application Ser. No. 60/649,849, filed Feb. 2, 2005. The identified earlier-filed applications are hereby incorporated by reference into the present application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of marine equipment, particularly, the art of connecting tugboats or pusher vessels with barges or other non-powered vessels which are equipped with a notch in the stern of the barge for receiving a tug or pusher vessel therein.

2. Description of the Prior Art

Barges are used to transport cargo on water, but have no self-propelling mechanisms, and rely primarily on tugboats or other pusher vessels for movement from one location to another. There exist many types of connections for coupling tugboats to barges, and the particular form of connection used depends on the marine environment in which the transportation takes place. As can be expected, a more secure coupling arrangement is required to maintain the connection of the tugboat to the barge in rough waters. For example, when a barge is used to transport oil, the coupling of the tugboat to the barge, the loading of the barge, and the actual pushing of the loaded barge take place out in open sea and are subject to substantial waves. It is imperative that the tug boat be securely connected to the barge to prevent the tug boat from being tossed about against the barge, or substantial damage and injury can occur.

A stable form of connection is provided through the use of extendable ram devices on the tug boat which interconnect with receivers on the barge. An example of this extendable ram and receiver configuration is shown in FIGS. 1 and 2 wherein a tug boat or pusher vessel 14 is connected to a barge 10. This connection is achieved by the bow of tug 14 entering a generally U-shaped or V-shaped notch 12 on barge 10. Once the tug 14 is within notch 12, rams 16 are extended from tug 14 into receivers 18 of the barge 10. The connecting rams typically have a drive mechanism that will generate sufficient force to securely hold tug 14 within notch 12 of barge 10. A connection of this type is shown in U.S. Pat. No. 3,512,495 to Fletcher in which a hydraulically extendable shaft is mounted on the port and starboard sides of the bow of the tug boat, and the cylindrical shaft of the tug is inserted into a circular receiver or housing mounted on the port and starboard walls of the notch within the barge.

This type of connection is suitable when the barge maintains a fixed load and the tug boat merely transports the barge. However, a tug boat must frequently transport a barge to a first destination where it receives a load, and then transport the barge to a second destination where the barge is unloaded. During the two operations, the respective water levels of the tug boat and barge will change relative to each other as the load weight is affected. For example, when the barge is empty, it will sit in the water relatively high. As the barge is loaded, the weight of the load will cause the barge to sit lower in the water. However, because no weight change is made to the tug boat itself, the water line of the tug boat remains constant. If the tug boat were to remain fixedly connected to the barge during the loading operation, the weight load would push the tug boat down into the water, with possibly disastrous consequences. The tug boat must, however, maintain some degree of connection with the barge during loading, otherwise the waves from the rough waters may prevent realignment and re-attachment. Therefore, the connection must permit the relative levels of the tug boat and barge to change as the weight load varies. The process by which the tug boat adjusts its position to the coupled barge as the weight load is changed is called lightering.

As shown in FIG. 1, certain coupler systems provide vertical channels 20 on the port and starboard sides of notch 12 in barge 10 for receiving the rams 16. A coupler system of this type is shown in U.S. Pat. No. 4,688,507 to Kuhlman et al. The vertical channels 20 extend along the top to bottom height of barge 10 and have a wedge shape configuration which opens up in an inboard direction. Rams 16 are provided with a coupler head 22 having a similar wedge shape configuration, as shown in FIGS. 3 and 4, which are oriented on the rams to mate with the wedge shape configuration of the vertical channels 20. A series of teeth 24 are arranged along the sidewalls of the vertical channels 20 as shown in FIGS. 6 and 7. Similarly, a series of teeth 26 are arranged along the lateral sides of ram coupler heads 22 as shown in FIG. 4. As ram heads 16 are extended and brought into engagement with vertical channel receivers 20, their respective teeth interlock. The depth of the teeth permit sufficient engagement to prevent relative vertical movement of the tug boat with respect to the barge.

To permit the relative vertical movement of the barge with respect to the tug boat, the rams are retracted a sufficient distance so that the teeth 26 of coupler head 22 come out of interlocking engagement with the teeth 24 of vertical channel receiver 20. The distance of retraction must be enough so that the tips of teeth 26 can clear the tips of teeth 24 so relative vertical movement can occur. Any contact between the tug coupler head and the barge during vertical motion with this type of connection causes the tug ram to turn and makes reengagement difficult. Full disconnection is required to allow relative vertical movement between the tug and barge. The operation of the rams is mechanically and electrically controlled as fully explained in the Kuhlman et al U.S. Pat. No. 4,688,507 and is now well known to those having skill in the art.

Full disconnection results in loss of longitudinal and tug roll control. Any time the ram disengages from secure engagement with the receiver, there is potential for mishap, especially in the heavy waters out at sea. Specifically, anytime that the coupler becomes disengaged, the tug boat is allowed to roll.

Accordingly, it is desirable to minimize the degree of disengagement of the ram from the receiver channel during the lightering operation so that the ability for respective vertical movement between the tug boat and barge is maximized, while the potential for tug boat roll and loss of longitudinal control is minimized. It is also desirable to minimize the amount of time it takes to disengage the ram coupler head from engagement with the receiver channel long enough for the lightering adjustment to be made, then to reengage the ram coupler head with the receiver channel to reestablish a secure connection.

SUMMARY OF THE INVENTION

In accordance with one embodiment, the invention comprises a tug barge lightering connection system of the type comprising a ram equipped with a coupler head for engagement with a vertical receiver channel of a barge, which is adapted to minimize the degree of disengagement of the ram from the receiver channel during the lightering operation so that the ability for achieving respective vertical movement between the tug boat and barge during the lightering operation is maximized, while the potential for unintentional longitudinal movement is minimized. The coupler head of the tug boat ram is wedge shaped and its lateral edges are provided with a waveform surface. The vertical receiver channels of the barge have a complementary wedge shape for receiving the ram coupler heads. The opposing side walls of the vertical receiver channels also have a waveform surface that mates with the lateral edges of the ram coupler heads as they come into engagement with the receiver channels. The waveform surface of the respective coupler heads and sidewalls of the receiver channels thus permit an interlocking engagement to provide a secure vertical connection between the tug boat and barge. The smooth curves and the absence of angular edges in the waveform surface of the respective coupler heads and sidewalls permit smooth incremental relative vertical movement of the tug boat to the barge during the lightering operation. The low amplitude of the waves also minimize the degree of ram disengagement from the receiver channels necessary to effect vertical movement. The wedge shape entry point of the receiver channels provide sufficient area for the retraction of the waveform surface of the coupler heads to disengage from interlocking connection with the waveform surface of the receiver sidewalls while still providing longitudinal control of the connection between tug boat and barge.

In accordance with another aspect of the invention, the shape of the waveform on the lateral edges of the coupler heads and the sidewalls of the vertical receiver channels may vary depending upon the weight load to which they are subjected. The greater the load transported by the barge, the greater the amplitude of the wave may be desired at any given level of ram engagement pressure. The waveform surface of the vertical channels may be comprised of discrete sections which can be attached onto the sidewalls of vertical receiver channels in barges.

Accordingly, it is an object of the present invention to provide a lightering connection system between a tug boat and a barge for maximizing the vertical relative movement efficiency between a tug boat and a barge during the lightering operation, while minimizing the loss of secure connection between the tug boat and the barge during the lightering operation. There has thus been outlined herein, rather broadly, certain embodiments of the invention in order that the detailed description thereof may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a side elevation view of a tug boat interconnected with a barge.

FIG. 2 is a plan view of a tug boat interconnected with a barge by insertion of the tug boat within the notch of the barge and showing the orientation of the rams on a tug boat within the receivers of the barge.

FIG. 3 shows a tooth style coupler head and ram to which it is connected.

FIG. 4 is a front elevational view of the ram coupler head of FIG. 3.

FIG. 5 is a breakaway cross-sectional plan view of the tug boat and the driving mechanism for extending and retracting the rams.

FIG. 6 is a front elevational view of a tooth style receiver channel on a barge for receiving a ram equipped with a tooth style coupler head.

FIG. 7 is a fragmentary cross-sectional view taken along line 7-7 of FIG. 6 and showing the arrangement of the teeth on the tooth style receiver channel.

FIG. 8 is a fragmentary cross-sectional view of the waveform surface of the helmet and receiver channel vertical faces of the present invention.

FIG. 9 is a fragmentary plan view of a tug boat interconnected with a barge by insertion of a ram and helmet of the tug boat within the vertical receiver of the barge according to an embodiment of the present invention.

FIG. 9A is a fragmentary cross-sectional view taken along line 9A-9A of FIG. 9.

FIG. 10 is a plan view showing the lightering operation required retraction of a ram of the tug boat within the vertical receiver of the barge according to an embodiment of the present invention.

FIG. 10A is a fragmentary cross-sectional view taken along line 10A-10A of FIG. 10.

FIG. 11A is a fragmentary cross-sectional view showing the close engagement between the respective waveform surfaces of the ram coupler head and the wall of the receiver channel according to an embodiment of the present invention.

FIG. 11B is a fragmentary cross-sectional view showing the relationship between the respective waveform surfaces as the coupler head is retracted from the receiver channel during lightering operations.

FIG. 11C is a fragmentary cross-sectional view showing the relationship between the respective waveform surfaces as the crests of the coupler head waveform pass over the crests of the receiver channel waveform during lightering operations.

FIG. 11D is a fragmentary cross-sectional view showing the relationship between the respective waveform surfaces as the coupler head is extended back into the receiver channel preparing to secure from lightering operations.

FIG. 11E is a fragmentary cross-sectional view showing the reengagement to the secure connection of the respective waveform surfaces of the ram coupler head and the wall of the receiver channel.

FIG. 12 is a perspective view of the vertical channel receiver of a barge incorporating the waveform surface according to an embodiment of the present invention.

FIG. 13 is a cross-sectional view of the vertical channel receiver taken along line 13-13 of FIG. 12.

FIG. 13A is a cross-sectional view of a sidewall of the vertical channel receiver taken along line 13A-13A of FIG. 13.

FIG. 14 is a front elevational view of the ram coupler head according to an embodiment of the present invention.

FIG. 15 is a cross-sectional plan view of the coupler head as partially engaged with the vertical receiver channel during lightering operations.

FIG. 16 is a cross-sectional plan view of the coupler head as fully engaged with the vertical receiver channel.

FIG. 17 is a cross-sectional plan view of the coupler head as mounted on the ram.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings in more detail, FIG. 8 generally shows the waveform surface of the present invention. Unlike the tooth-like projections of the prior-art coupling systems, waveform surface 30 is comprised of rounded projections 31. This permits an opposing surface of similar configuration to move smoothly over the projections. Angular, non-rounded edges are avoided. The waveform surface should have consistent amplitude and pitch dimensions, amplitude (A) being defined herein as the height of the wave crests, and pitch (P) being defined as the distance between wave crests as shown in FIG. 8. The optimum amplitude may vary depending on the weight load involved in the lightering operation, but frictional forces and compressive forces provided by the tug boat rams will play a significant role as well. In any event, the amplitude must be a value greater than zero, but have a value less than the pitch. Preferably, the ratio of the amplitude to pitch should be about 1:7.

Waveform surfaces 32 and 34 are provided on the lateral sides 36 and 38 of coupler head, or helmet, 40, respectively, as shown in FIG. 14. The lateral edges of the coupler head 40, when viewed in plan from above, are angularly disposed towards each other and converge slightly at the front of the coupler head, as best shown in FIG. 17. Vertical channel receiver 42 comprises sidewalls 44 and 46 which generally oppose each other, but diverge outwardly from each other towards the channels opening, as shown in FIGS. 12 and 13. As can be seen in FIGS. 15 and 16, the angular orientation of the coupler head is complementary to the angular orientation of the vertical channel receiver 42. Wave form surfaces 50 and 52 are provided on side walls 44 and 46, respectively. The wave form surfaces may be integrally welded as a single piece directly on the side wall, or may be provided in sections which are then attached to the side wall. When adjacent sections are abutted against each other, it is important to ensure that the connection joint 54 be smoothed down to avoid any obstructions or raised areas that detract from the smooth waveform surface, as shown in FIG. 13A. As well understood by those having skill in the art, the function, structure and arrangement of the laterally positioned rams and the configuration of their respective coupler heads are analogous with respect to the port side and the starboard side of the tug boat. Similarly, the vertical receiver channels on port and starboard sides of the barge vessel are essentially identical to each other, except for orientation. Accordingly, discussion relating to structures for the coupler heads and vertical receiver channels herein will be understood to be applicable to the connection system for both the port and starboard positions.

The interaction between the waveform surfaces on the ram coupler head and sidewalls of the vertical channel receiver can be understood by viewing the operation as referenced in the drawings and aided by the following description. In the usual barge transportation scenario, a tug boat 14 enters the notch 12 of a barge 10 equipped with port and starboard vertical receiver channels of the type well known in the art, as shown in FIGS. 1, 2 and 5. Rams 56 and 58 are powered to extend coupler heads 40 and 60, respectively, from tug boat 14 so that they enter vertical channel receivers 42 and 62, respectively. As can be seen in FIG. 10, the fore and aft sidewalls 46 and 44 help control longitudinal movement of the tug boat within the notch of the barge. However, until the waveform surfaces of coupler head 40 engage the waveform surfaces of the sidewalls of receiver channel 42, there is no vertical control. FIG. 10A shows waveform surface 34 of lateral side 38 of coupler head 40 apart from waveform surface 50 of sidewall 44 of vertical channel receiver 42. This is the condition present as the coupler head enters the receiver channel. As the ram is fully extended, coupler head 40 engages completely with vertical channel receiver 42, and the lateral edges 38 and 36 of coupler head 40 bear against vertical channel side walls 44 and 46 respectively. FIG. 9A shows waveform surface 34 of lateral side 38 of coupler head 40 nestled within waveform surface 50 of sidewall 44 of vertical channel receiver 42. In this condition, vertical control is fully effected, and the relative vertical positions of the tug boat and barge should remain the same, provided a sufficient amount of extension force is placed against the rams.

FIGS. 11A-11E show the interaction of the waveform surfaces of the coupler heads with the waveform surfaces of the sidewalls of the vertical channels over one cycle of movement that takes place during the lightering operation. In FIG. 11A, the respective waveform surfaces of coupler head 38 and vertical channel sidewall 44 are in complete engagement, brought about by full extension of the ram against the vertical channel as shown in FIG. 16. As cargo is deposited into the barge, its weight will increase and cause the barge to descend and lie lower in the water. As that occurs, the tug boat must release its connection otherwise it will be dragged down into the water as well. FIG. 11B shows, with the release of extension force by the ram, the primary waveform surface of coupler head 38 beginning to disengage from the secondary waveform surface of vertical channel sidewall 44, as shown in FIG. 15. As this occurs, the incrementally greater weight of the barge causes the vertical channel sidewall 44 to move downward relative to coupler head 38. FIG. 11C shows the crest of the waves of the secondary waveform surface of vertical channel sidewall 44 sliding over the crest of the waves of the primary waveform surface of coupler head 38. Assuming that the weight differential has been settled, the rams are again extended to regain vertical movement control. In FIG. 11D, as the rams are extended, the waveform surfaces are again brought into engagement. When lightering equilibrium is reached, the rams are extended to lock the waveform surfaces of the coupler head and vertical channel sidewall in locking engagement as shown in FIG. 11E and FIG. 16. In this fashion, the waveform surfaces of the present invention provide close control over vertical movement between tug boat and barge, while minimizing loss of horizontal control. During the entire lightering operation as depicted in FIGS. 11A-11E, coupler head 40 is able to remain in the confines of vertical channel 42, as seen in FIGS. 15 and 16, to prevent forward or backward motion of the tug boat relative to the barge. The relationship between the depth of the vertical channel receiver 42 and amplitude of the wave crests should be such that when the primary and secondary waveform surfaces 34 and 50 are moved apart for lightering operations as shown in FIG. 10A, a sufficient amount of coupler head 40 remains within the vertical channel receiver 42 as shown in FIG. 10.

The waveform surface also permits vertically controlled movement as a function of friction. With the rounded surfaces provided by the waveform, the transition between the point where a wave crest emerges out of a trough (as in FIG. 11B), moves over an opposing wave crest (as in FIG. 11C), and descends back towards another wave trough (as in FIGS. 11D and 11E) is able to occur more smoothly with the lower amplitude of the wave crest. It is critical that reengagement of the coupler head in tight compression with the receiver channel take place as quickly as possible because the tug boat is subject to roll whenever the vertical restraint of the connection is disengaged.

As shown in FIG. 17, coupler head 40 is shown in cross-sectional view as seated on the end of ram 56. Support ball 66 is a steel ball and coupler head 40 is secured thereto by the attachment of a circumferential securing plate 68. The securing plate forms a collar which retains coupler head 40 on support ball 66. Support ball 66 acts as a swivel for coupler head 40 and allows coupler head 40 to move to allow coupler head 40 and receiver 42 to self-align.

One embodiment of the waveform surface of the present invention comprises a coupler head whose lateral sides have the waveform surface integrated therein. This enables existing rams using a helmet incorporating the tooth-edged coupler to be switched with a helmet incorporating the waveform surface coupler. Similarly, the vertical channel receiver may have the waveform surface integrated into its sidewalls. Alternately, the waveform surface could be connected to an existing surface by welding or bolting or the like. Another embodiment provides for the waveform surface to be installed on vertical channel receiver side walls by installing in individual sections as shown in FIG. 12. For example, individual plates can be manufactured and aligned together over the length of the side wall. Each plate can incorporate a waveform having four cycles of waves to provide four wave crests. A typical wave plate incorporating four wave crests would have a width of 20 inches and a length of 28 inches, with each wave crest having a height of one inch. If desired, wave plates having more than or fewer than four wave crests can be manufactured.

In the foregoing description, certain terms have been used for brevity, clearness and understanding; but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such terms are used for descriptive purposes and are intended to be broadly construed. Moreover, the description and illustration of the inventions is by way of example, and the scope of the inventions is not limited to the exact details shown or described.

Certain changes may be made in embodying the above invention, and in the construction thereof, without departing from the spirit and scope of the invention. It is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not meant in a limiting sense. Having now described the features, discoveries and principles of the invention, the manner in which the inventive tugboat and barge connector and receiver combination is constructed and used, the characteristics of the construction, and advantageous, new and useful results obtained; the new and useful structures, devices, elements, arrangements, parts and combinations, are set forth in the appended claims.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween. 

1. A coupler and receiver assembly for connecting a pusher vessel within a stern notch of a barge, the assembly comprising: a pair of rams provided on lateral sides of the pusher vessel, a coupler head attached to each of the rams, receiver channels for receiving each coupler head provided on the barge, each receiver channel comprising first and second generally opposed sidewalls, each of the coupler heads comprising lateral edges, at least one of the lateral edges of each coupler head having a primary waveform surface with a plurality of rounded, non-angular projections, at least one of the first and second sidewalls of each of the receiver channels having similar secondary waveform surfaces adapted to mate with the lateral edge of the coupler heads having the primary waveform surface.
 2. The coupler and receiver assembly of claim 1 in which the pusher vessel is adapted for engagement with the barge when the primary waveform surfaces of the lateral edges of the coupler heads mate with the secondary waveform surfaces of the receiver channels such that crests of a wave of a first waveform surface lie completely within troughs of an opposing second waveform surface.
 3. The coupler and receiver assembly of claim 1 in which the sidewalls of the receiver channels are angularly disposed towards each other such that longitudinal planes in which the sidewalls lie diverge outwardly each from each other, and the lateral edges of the coupler heads are angularly disposed towards each other such that longitudinal planes in which the lateral edges lie diverge towards each other towards a front of the coupler head.
 4. The coupler and receiver assembly of claim 1 in which the rams are adapted for automated extension and retraction to effect engagement and disengagement of the pusher vessel with and from the barge, respectively.
 5. The coupler and receiver assembly of claim 3 in which the rams are adapted for extension and retraction to effect engagement and disengagement of the pusher vessel with and from the barge, respectively, the amplitudes of waves of the primary and secondary waveform surfaces having a combined value less than a distance equal to that necessary for the coupler heads to be completely withdrawn from the receiver channels.
 6. The coupler and receiver assembly of claim 5 in which relative vertical movement between the pusher vessel and barge is enabled when the crests of waves are completely withdrawn from troughs of opposing waveform surfaces.
 7. The coupler and receiver assembly of claim 6 in which relative horizontal movement of the pusher vessel is limited when the coupler heads are at least partially within the receiver channels.
 8. The coupler and receiver assembly of claim 7 in which the primary waveform surface is provided on both lateral edges of the coupler heads, and the secondary waveform surfaces are provided on both the first and second sidewalls of the receiver channels.
 9. The coupler and receiver assembly of claim 1 in which the respective waveform surfaces of the lateral edges of the coupler heads and the sidewalls of the receiver channels have an amplitude greater than zero, but less than a value representing a distance of a pitch of the waveform.
 10. The coupler and receiver assembly of claim 9 in which a ratio of the amplitude to pitch is 1:7.
 11. A coupler and receiver assembly for maintaining a water level position of a pusher vessel within a stern notch of a barge during a lightering operation, the assembly comprising: a pair of rams provided on lateral sides of the pusher vessel, a coupler head attached to each of the rams, the coupler head having lateral edges angularly disposed towards each other at the front end of the coupler head, receiver channels for receiving each coupler head provided on the barge, each receiver channel comprising first and second generally opposed sidewalls, the sidewalls being angularly disposed away from each other at the longitudinal opening of the receiver channel, the angular disposition of the sidewalls being equal but opposite to the angular disposition of the lateral edges of the coupler head, each of the coupler heads comprising lateral edges having a primary waveform surface with a plurality of rounded, non-angular projections, each of the first and second sidewalls having similar secondary waveform surfaces with a plurality of rounded, non-angular projections adapted to mate with the lateral edges of the coupler heads, the rams being adapted for extraction and retraction to maneuver the coupler heads into engagement with and disengagement from the receiver channels, whereby the primary waveform surfaces of the lateral edges of the coupler heads are capable of being brought into mating engagement with the secondary waveform surfaces of the first and second sidewalls of the receiver channels to secure the pusher vessel within the stern notch of the barge.
 12. The coupler and receiver assembly of claim 11 in which the pusher vessel is restricted from relative vertical movement with respect to the barge when crests of a wave of a first waveform surface lie completely within troughs of an opposing second waveform surface.
 13. The coupler and receiver assembly of claim 12 in which the barge is adapted for relative vertical movement with respect to the pusher vessel when the barge is subject to load variations, the rams being adapted for retraction to bring the crests of the wave of the first waveform surface out of engagement with the troughs of the opposing second waveform surface, the coupler heads and receiver channels being adapted to slide with respect to each other in a vertical direction when the crest of the first waveform surface is not overlapping the crest of the second waveform surface.
 14. The coupler and receiver assembly of claim 13 in which relative horizontal movement of the pusher vessel is limited when the coupler heads are at least partially within the receiver channels.
 15. The coupler and receiver assembly of claim 11 in which the respective waveform surfaces of the lateral edges and sidewalls have an amplitude greater than zero, but less than a value representing a distance of a pitch of the waveform.
 16. The coupler and receiver assembly of claim 15 in which a ratio of the amplitude to pitch is 1:7.
 17. An assembly for coupling a first vessel with a second vessel, the assembly comprising: a ram provided on the first vessel; a coupler head attached to the ram; and a receiver channel provided on the second vessel for receiving the coupler head, with the receiver channel including first and second sidewalls, wherein the coupler head includes first and second lateral edges, with at least one of the lateral edges having a primary waveform surface presenting a plurality of curved, non-angular projections, and at least one of the first and second sidewalls of the receiver channel having a similar secondary waveform surface adapted to mate with the lateral edge of the coupler head having the primary waveform surface.
 18. In a system for selectively coupling a first vessel with a second vessel, wherein the system includes— a first ram including a first coupler head, the first ram being mounted on the first vessel so as to be selectively extendable outwardly from a first side of the first vessel; a first receiver channel provided on a first side of a notch in the second vessel, oriented substantially vertically, and operable to receive the first coupler head when the first vessel is located within the notch and the first ram is extended; a second ram including a second coupler head, the second ram being mounted on the first vessel so as to be selectively extendable outwardly from a second side of the first vessel; and a second receiver channel provided on a second side of the notch in the second vessel, oriented substantially vertically, and operable to receive the second coupler head when the first vessel is located within the notch and the second ram is extended; the improvement comprising: the first and second coupler heads each having left and right sides, with each of the left and right sides including a coupler head surface presenting a first plurality of low amplitude, rounded projections; and the first and second receiver channels each having left and right sides, with each of the left and right sides including a receiver channel surface presenting a second plurality of low amplitude, rounded projections, wherein the first and second pluralities of low amplitude, rounded projections interact so as to allow for vertical sliding movement between each coupler head and its respective receiver channel without requiring full withdrawal of the coupler head from the receiver channel, thereby allowing for relative vertical movement between the first and second vessels while substantially eliminating other relative movement. 